4. SUMMARY AND FUTURE WORK

We have reviewed the current observational status of the M87 jet, as
well as several
models and problems suggested by the data. To briefly summarize:

High resolution observations show the jet is well collimated on
scales from about 1
to 1000 pc, with evidence collimation extending down to scales ~ 0.01
pc. Beyond
1 kpc the jet passes through "shock-like" structures, becomes unstable
and poorly collimated, but yet continues to scales ~ 35 kpc.

The optical and X-ray morphology of the 25" (2 kpc) jet, except for
a few systematic
trends, is nearly identical to the radio morphology. Knots along the
inner jet have
similar radio-to-optical spectra, thus creating the "particle lifetime"
problem.

Comparison of radio images from different epochs give evidence for
proper motions
with typical apparent speeds between 0.5c and 1.0c. Speeds
up to 3c are seen for the inner jet.

The recent discovery of an optical continuum hot spot opposite the
jet strongly suggests a counter-jet is present.

The emission regions within the jet appear to be out of pressure
balance with the
surrounding interstellar medium. It is possible that some of these
regions are freely
expanding, while others may be shocks. The most serious confinement problems
appear in knot B, and magnetic effects may be able to provide confinement.

It is difficult to produce the observed radio-to-X-ray spectrum
with existing models.

We have outlined a kinematic model wherein the first kpc of the jet
moves with a
relativistic velocity ( 3). The jet is then
slowed at several shocks, and finally
proceeds outward to distances ~ 35 kpc at sub-relativistic speeds. In
this model the inner jet is aligned about 40° from the line of
sight.

Future VLA observations, as well as monitoring with HST, are needed to confirm
the observed motions. As speeds are measured for more regions, it may be
possible
to assemble and observed flow diagram, and hence perform detailed tests
of numerical
models. VLBI monitoring may clarify the situation at pc-scales, where
low velocities
have been seen. Combined radio, infrared, optical, UV, and X-ray
observations at
similar resolution ( 1")
are needed to assemble a detailed spectrum of the jet, both in
the knots and inter-knot regions. This may elucidate the cause of the
optical spectral
break and the process responsible for the X-rays. Theoretical and
numerical models
are needed which address the possibility of relativistic flow for the
inner jet, and the
consequences this may have for M87 and other FR-I sources.